The present invention relates to lasers, and more particularly, to an improved surface emitting laser diode.
Semiconductor laser diodes were originally fabricated in a manner that led to a diode structure that was parallel to the surface of the semiconductor wafer. In this structure, light is emitted from the edge of the structure such that the light was also emitted parallel to the surface of the semiconductor wafer. Unfortunately, this structure does not lend itself to the cost-effective fabrication of arrays of laser diodes.
A second class of laser diodes is fabricated such that the laser structure is perpendicular to the surface of the semiconductor wafer and the light is emitted perpendicular to the surface. These laser diodes are commonly known as surface emitting lasers (SELs). These lasers are better suited for the fabrication of arrays of lasers for displays or driving arrays of optical fibers.
It would be advantageous to be able to operate large area SELs in the higher order transverse modes. This requires high current injection levels. The high current injection can lead to a reduced lifetime for the SEL. In addition, the modes are not always reproducible from device to device.
In general, SELs have a threshold potential that must be applied to obtain light output. In large area SELs, filaments appear at potentials near the threshold. Each filament is a small lasing region. As the potential is increased, the number of filaments increases until the entire area of the SEL produces light by the joining of the various filaments. The locations at which these filaments are initiated and the density of filaments are not predictable in prior art devices.
Broadly, it is the object of the present invention to provide an improved large area SEL.
It is a further object of the present invention to provide an SEL in which filament initiation and density are more easily controlled.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is a SEL having a light generation and first and second mirror layers. The first and second mirror layers reflect light generated in the light generation region back toward the light generation region. Each of the mirrors reflects light such that it adds coherently to the light generated in the light generation region or light reflected from the other mirror. In the preferred embodiment of the present invention, one of the mirrors includes a localized imperfection which causes light interacting therewith to be attenuated or shifted in phase relative to light that does not interact with the imperfection region. As a result, lasing filaments are preferentially initiated in the regions adjacent to the localized imperfection.